A device of the type mentioned by way of introduction is known from U.S. Pat. No. 5,372,229. Said patent publication discloses a chute for mechanical guiding of pieces or particles of material, said chute having two or more chute elements mounted substantially coaxially above each other and connected by flexible connecting devices and designed to be telescopically mutually stackable. An advantage of conveying a material through a chute compared with letting it fall freely is that the large amounts of dust that would otherwise occur will be reduced. In a telescopic chute, the falling material generates a pressure below atmospheric in the chute, whereby air is drawn into the space between the chute elements and dust is prevented from being spread. The construction of a telescopic chute as described above also gives increased flexibility compared with fixedly mounted chutes since a telescopic chute can easily be raised and lowered as required. This is particularly important when the chute is used for conveying a material consisting of several size fractions. If the distance between the mouth of the chute and the bulk heap is not short and constant, variable sorting of the material will take place, for instance caused by the wind effect. As a rule, the height of the chute is adjusted by ropes or wires, which pass through guides on some of the chute elements or all chute elements and are attached to the lowermost chute element, being used to lift the lowermost chute element. If the distance of lifting exceeds the distance between neighbouring chute elements, the chute elements will gradually be mutually stacked from below and up.
However, when using telescopic chutes of the type described above, problems with local wear are frequently experienced, when, for instance, a certain fraction of material continuously hits one and the same point on one and the same chute element and, thus, wears a hole in the same. Such local wear is unpredictable in the sense that you cannot know for sure where, that is on which surface of which chute element, it will occur. Known telescopic chutes suffer from the drawback that when local wear occurs, you cannot easily repair a separate chute element. In case of local wear, the entire chute element is generally replaced, and the worn one is discarded.
A possible solution would be to make the whole chute from an extremely abrasion resistant material from the beginning, which however is not done for several reasons. The first reason is that a more abrasion resistant material in general is synonymous with a heavier material, and since the chute generally is suspended from the outermost end of another structure, for instance a conveyor, the increased weight will cause a problem. Another reason is that if the chute is much more abrasion resistant than the material that is being conveyed, the material will be disintegrated into smaller fractions, which in general is not desirable. A third reason is that, as a rule, the same material properties are not desirable through an entire chute. For example, a shock-proof material is desired at the top of the chute while for chute elements further down in the chain, greater resistance to wear is more important. In addition to that mentioned above, also a cost aspect is to be taken into consideration.
Also chute elements that are square in cross-section are previously known, for instance from U.S. Pat. No. 345,039.